Vol 59, No 11 (2017)

In this work, using the non-Hermitian Hamiltonian method, the transmission of a single photon in a one-dimensional waveguide interacting with the cavity containing an arbitrary number of photons and the two-level artificial atom is studied with allowance for the relaxation of the latter. For transport factors, analytical expressions which explicitly take into account the qubit relaxation parameter have been obtained. The form of the transmission (reflection) coefficient when there is more than one photon in the cavity qualitatively differs from the single-photon cavity and contains the manifestation of the photon blockade effect. The qubit lifetime depends on the number of photons in the cavity.

The effect of ultrasound on motion of the Frenkel–Kontorova dislocations in aluminum has been studied with inclusion of the Peierls relief. A dislocation moves at a variable rate when overcoming the Peierls barrier. The dislocation mean free path is changed under action of ultrasound at various frequencies comparable to the dislocation transition time to a neighboring valley. The stress–strain dependences have been obtained for high and low strain rates. In both the cases, a disordering takes place; however, the disordering rates and characters are different. At the resonance frequency, the strain resistance decreases, the hardening stage is shortened and the disordering stage is elongated. The dependence of the coefficient of hardening on coordinate has three segments different in characters. The coefficient of hardening decreases at the resonance frequency.

The influence of high pressure on the structure of amorphous alloys based on aluminum, iron, and cobalt is studied by X-ray diffraction, scanning, and transmission electron microscopy. It is found that the exposure of the alloys to a pressure of 5–8 GPa at room temperature leads to various changes in amorphous structures in the dependence on the alloy compositions: separation of initially homogeneous amorphous phase and the formation of a nanoglass, formation of nanocrystals, or does not cause any marked changes in the structure. It is shown that the differences in the deformed structures of the amorphous phase of aluminum- based alloys and alloys based on iron and cobalt are due to different values of the elastic constants of these groups of alloys and different temperature crystallization of the amorphous phase. It is shown that the value and the time of the pressure influence are important factors that determine the change in the amorphous structure and the formation of nanocrystals.

The current–voltage characteristics of superconductor–insulator–semiconductor (S1–I–S2) tunnel junctions, where superconducting electrode S2 is a thin nanowire, are studied experimentally. The observed blurring of the gap singularities is interpreted as a manifestation of the order parameter quantum fluctuations. We propose a model taking into account the broadening of the density of states due to the interaction of electrons with the Mooij–Schön plasmon mode emerging in a quasi-one-dimensional superconducting channel in the regime of quantum fluctuations of the order parameter. The model gives results that are in a reasonable qualitative agreement with the experimental data.

We investigate the effect of the intersite Coulomb interaction in a planar system with the triangular lattice on the structure of chiral order parameter Δ(p) in the phase of coexisting superconductivity and noncollinear 120° magnetic ordering. It has been established that the Coulomb correlations in this phase initiate the state where the quasi-momentum dependence Δ(p) can be presented as a superposition of the chiral invariants corresponding to the \({d_{{x^2} - {y^2}}} + i{d_{xy}}\) and p_x + ip_y symmetry types. It is demonstrated that the inclusion of the Coulomb interaction shifts the Δ(p) nodal point positions and, thereby, changes the conditions for a quantum topological transition.

The paper presents a new etching-free technology for the formation of planar superconductor structures based on YBCO films with metal contacts. The required topology of superconducting elements from YBCO film is created by the proposed “preliminary topology mask” method. The ohmic contacts to the superconducting structure are produced by lift-off photolithography. In order to study the capabilities of this technology, measurements of superconducting bridges with a width of 3, 10, and 50 μm and test structures for measuring the contact resistance are performed.

Calculations of critical temperature T_c of the phase transition to superconducting state of a superconductor/ ferromagnet/superconductor (SFS) hybrid structure with proximity effect is performed on the base of linearized Usadel equations. It is shown that the proximity effect between S and F metals and the exchange interaction can induce an inhomogeneous superconducting state with longitudinal to layers Δ _∝ exp(ipz) modulation of the superconductivity order parameter, which is characterized by nonzero value of the wave number p, describing the Larkin–Ovchinnikov–Fulde–Ferrell instability. Influence of this instability on transitions between 0- and π-states of the SFS structure is studied. It is shown that the 0–π transition is accompanied by a nonmonotonic dependence of both the critical temperature T_c and the effective penetration depth Λ of the magnetic field into the hybrid structure on the characteristic size of the ferromagnetic region.

Laser annealing experiments were performed in order to increase the concentration of electrically active manganese in the layers of A³B⁵: Mn semiconductors. An LPX-200 KrF excimer laser with a wavelength of 248 nm and a pulse duration of ~30 ns was used. It is shown experimentally that at a pulse energy of an excimer laser of >230 mJ/cm², the hole concentration in GaAs: Mn layers increases to 3 × 10²⁰ cm^–3. The negative magnetoresistance and the anomalous Hall effect with a hysteresis loop for annealed GaAs: Mn samples remain the same up to 80–100 K. Similar changes are observed for InAs: Mn layers as a result of laser annealing.

Circularly polarized luminescence of light-emitting InGaAs/GaAs structures with a delta-doped Mn layer in a GaAs barrier was studied. The structural parameters were varied by different ways, among them are homogeneous and delta-doping with acceptor impurity, and removal of donor doping from the technological process. As it was found, the magnitude and polarity of the degree of circular polarization of luminescence strongly depend on the technological mode chosen. Simultaneous modeling of wave functions of structures highlights a good agreement between the parameters of circularly polarized luminescence and spatial distribution of wave functions of heavy holes relative to the Mn delta-layer.

Volumes of the metastable Si-II, Si-XII, Si-III, and α-Si silicon phases in a locally deformed (Berkovich pyramid) region of unirradiated and beforehand irradiated Si single crystals are quantitatively estimated. Experimental data obtained by Raman spectroscopy and in situ detection of Si-I → Si-II silicon phase transformations under an indenter are used to calculate the volumes. The preliminary irradiation of silicon by β particles from a ⁹⁰Sr–⁹⁰Y source (fluence F = 3.24 × 10¹⁰ cm^–2, intensity I = 1.8 × 10⁵ cm^–2 s^–1) reduces the volume of these phases by a factor of more than 1.5.

The effect of replacing manganese ions on the structural, dielectric, transport, and magnetic properties of Bi₂(Sn_0.9Mn_0.1)₂O₇ has been studied and the correlation between them has been determined. The change in the type of thermal processes and the thermopower sign upon polymorphous transitions were detected by differential scanning calorimetry. The paramagnetic Curie temperature and the antiferromagnetic interaction were determined in the martensite and austenite phases. The type of current carriers has been established.

Some results of the micromagnetic modeling of forced magnetization oscillations in planar microstrips of NiFe with easy plane anisotropy and Co/Pt with perpendicular easy axis anisotropy in the field of a magnetic spherical probe are considered. It has been shown that the probe field provokes the appearance of a hedgehog–antivortex coupling state in the NiFe strips, due to its lateral components and a skyrmion magnetization state in the Co/Pt layer. These effects destroy spatial magnetization oscillations in the microstrips and lead to the appearance of additional resonances in the spectrum of oscillations corresponding to the modes localized in the probe field.

The results of a micromagnetic simulation of the pinning-depinning processes of a domain wall (DW) in a rectangular ferromagnetic nanowire (NW) consisting of two magnetic layers with scattering fields of two rectangular two-layer nanoparticles (NPs) located on NW opposite sides and oriented perpendicular to its axis are presented. The features of magnetization reversal of this system in the external magnetic field are studied depending on direction of the magnetic moments of the nanoparticle layers. The value of the depinning field in such a system depends essentially on mutual orientation of NP magnetic moments and NW magnetization. The possibility to realize a magnetic logic cell performing the “conjunction” operation of ternary logic is discussed.

This is a complex study of the electrophysical and magnetic characteristics of epitaxial manganite La_0.7Ba_0.3MnO₃ (LBMO) films under conditions of crystal structure stresses caused by misfit in the lattice parameters of the LBMO crystal and a substrate. The substrate used had the lattice parameter smaller than that in the LBMO crystal. It is shown that the temperature dependence of the electrical resistance of the films at low temperatures is not dependent on the existence of stresses in the film and agrees well with the calculation with allowance made for the interaction of carriers with magnetic excitations in the presence of strongly correlated electronic states. The study of the ferromagnetic resonance line indicates an inhomogeneity of the ferromagnetic phase in the LBMO films and the increase in the ferromagnetic resonance line width with decreasing temperature.

Nanosized films with ferromagnetic layers are widely used in nanoelectronics, sensor systems and telecommunications. Their properties may strongly differ from those of bulk materials that is on account of interfaces, intermediate layers and diffusion. In the present work, spectral ellipsometry and magnetooptical methods are adapted for characterization of the optical parameters and magnetization processes in two- and three-layer Cr/NiFe, Al/NiFe and Сr(Al)/Ge/NiFe films onto a sitall substrate for various thicknesses of Cr and Al layers. At a layer thickness below 20 nm, the complex refractive coefficients depend pronouncedly on the thickness. In two-layer films, remagnetization changes weakly over a thickness of the top layer, but the coercive force in three-layer films increases by more than twice upon remagnetization, while increasing the top layer thickness from 4 to 20 nm.

The radiative and magnetic properties of novel heterostructures with a bilayer InGaAs/GaAsSb/GaAs quantum well and a GaMnAs ferromagnetic layer are studied. The circular polarization of electroluminescent radiation is observed at temperatures from 10 to 160 K. The magnetic field dependences of the degree of circular polarization are nonlinear with a hysteresis loop at temperatures from 10 to 50 K, and they become linear at higher temperatures. The magnitude of polarization at the saturation magnetization of GaMnAs in the 2000 Oe field remains at the level of ~0.2%.

Epitaxial InFeSb/GaAs heterostructures were obtained by laser deposition in vacuum. Investigations by high-resolution transmission electron microscopy and microdiffraction showed that the InFeSb layers are single-crystal and do not contain additional phase inclusions. Study of their magnetotransport properties have revealed that an anomalous Hall effect and a negative magnetoresistance up to room temperature are observed in the structures.

The effect of deformation on the electric properties in rare-earth garnet compounds is elucidated. It is shown that inhomogeneous deformation causes the emergence of electric polarization in garnet crystals on account of nonequivalent low-symmetry sites of rare-earth ions in the cubic structure of these crystals, whose symmetry of the environment has no inversion center. The polarization of a rare-earth ion subsystem in garnet crystals is studied upon the elastic wave propagation therein.

Triboluminescence bursts are observed in two heterogeneous (diorite) specimens under friction against each other. Triboluminescence appears upon the relaxation of excited free ≡Si–O^– radicals and Fe³⁺ ions and the capture of electrons with acceptor traps formed upon the destruction of the plagioclase crystal lattice. The analysis of the time dependence of these bursts shows that the friction surfaces accumulate clusters, in which the concentration of free ≡Si–O^– radicals and electron traps is at least an order of magnitude higher than in their surrounding. The time interval between the appearance of two sequential clusters variates from 0.1 to 1 μs. The linear sizes of clusters are ~0.5 μm.

The first principles study of the crystal structure, chemical bonds, elastic and mechanical properties, electron energy band structure and density, and normal long-wave vibrations of nine phases of lead monoxide, dioxide, and tetraoxide has been performed under normal and external pressure within the framework of density functional theory (DFT) with the Perdew–Becke–Ernzerhof (PBE) gradient exchange-correlation functional and its hybrid version with a 25-% Hartree–Fock (HF) exchange contribution in the basis of localized atom orbitals. The behavior of physical parameters has been studied using the cold four- and threeparameter equations of state. The parameters of the crystal structures are in satisfactory agreement with experimental data, and elastic constants indicate their mechanical stability and anisotropy in the elastic properties. The elasticity, shear, and Young moduli, hardness, acoustic velocities, and Debye temperature of dioxide on the one hand and monoxide and tetraoxide on the other hand appreciably differ from each other. The difference between electron properties may be explained by the character of hybridization in the upper filled and lower empty energy bands as evident from the density of states. In monoxide, the indirect band gap width decreases with increasing pressure at a rate of 0.16 eV/GPa, and the direct band gap width increases at a rate of 0.13 eV/GPa. To identify crystalline phases, the frequencies and intensities of long-wave modes active in IR and Raman spectra have been calculated.